High resolution, low cost, and miniaturization have been strongly demanded for imaging apparatuses mounted in mobile telephones, personal computers (PC), and the like in recent years.
The cell pitches of imaging elements such as CCD (Charge Coupled Device) and CMOS (Complementary Metal Oxide Semiconductor) image sensors and the like have been dramatically decreased, and optical systems are required to have high image forming performance that suppresses optical aberrations, particularly axial chromatic aberration more than ordinary optical systems.
However, when these problems are to be solved by only a lens system, the number of lenses is increased, and high assembly accuracy is required.
The problem of a need to make the lenses so small as to be unmanufacturable, for example, occurs.
One method for solving these problems is to curve an imaging element to reduce a need for image surface correction by the optical system, and simplify the lenses. A technology disclosed in Patent Document 1 is known as a typical example of the method.
In this example, in which a technology relating to optical design of a one-group, two-lens configuration is described, two plastic molds molded separately are laminated to each other, and a front diaphragm is formed. To be exact, a two-group, two-lens configuration is formed because of the presence of an air interval between groups. In addition, no infrared cutoff filter is inserted.